Inherited Disorders

This lesson covers two key inherited disorders — cystic fibrosis and polydactyly — along with genetic screening, testing, and ethical considerations. This is essential content for Edexcel GCSE Biology (1BI0) Topic 3: Genetics.

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Cystic Fibrosis

Cystic fibrosis (CF) is a genetic disorder caused by a recessive allele. It affects approximately 1 in 2,500 births in the UK.

Genetics of Cystic Fibrosis

• The allele for cystic fibrosis is recessive. We use f for the recessive (CF) allele and F for the dominant (normal) allele.
• A person must have two copies of the recessive allele (ff) to have cystic fibrosis.
• A person with one copy of the recessive allele (Ff) is a carrier — they do not have the disease but can pass the allele to their children.

Genotype	Phenotype
FF	Unaffected (not a carrier)
Ff	Unaffected but a carrier
ff	Has cystic fibrosis

Symptoms of Cystic Fibrosis